This disclosure relates generally to light emitting diode (LED) lighting systems and more particularly to light emitting diode light bulbs (LLB).
LLB bulbs have been developed that are interchangeable with conventional light bulbs having incandescent and fluorescent light sources. A LLB bulb typically includes a base, a power supply, a LED light source on the base having one or more LED light sources, and a lens/cover. Advantageously, LLB bulbs have higher conversion efficiencies, longer lifetimes and lower operating voltages than conventional light bulbs.
One aspect of LLB bulbs is that light reflection can occur from the inner or outer surface of the lens/cover. In particular, if the angle of incidence of light from the LED light source to the lens/cover is less than a critical angle, then light can be transmitted through the lens/cover. If the angle of incidence is greater than the critical angle, the light reflects from the lens back to the LED light source. In addition, a LLB bulb having a very bright LED light source, such as a packaged light emitting diode (PLED), can produce glare. Glare is unpleasant and makes it difficult for a person's eyes to see correctly. Briefly, glare is caused by a significant ratio of luminance between the task (that which is being looked at) and the glare source. Factors such as the angles between the task, the glare source and the eyes also have a significant impact on glare.
Glare can generally be divided into two types, discomfort glare and disability glare. Discomfort glare causes an instinctive desire to look away from a bright light source making the task more difficult to see. Disability glare renders the task impossible to view, such as when driving westward at sunset. Disability glare is often caused by the inter-reflection of light within the eyeball, reducing the contrast between the task and the glare source to the point where the task cannot be distinguished. When glare is so intense that vision is completely impaired, it is sometimes called dazzle. Because of bright glare from a LLB having a PLED light source, some LLB bulbs include lens/covers made of semi-transparent (ST) plastic or glass. However, these semi-transparent materials also reduce the light output of a LLB bulb. LLB bulbs can also have a lens/cover with a built in particle diffuser. Although particle diffusers reduce reflection, they also reduce the light output of the LLB bulb. The present disclosure is directed to LLB bulbs having a lens/cover with a light extraction surface that reduces glare and reflection with minimal light loss, producing improved light output from the LLB bulbs with reduced glare.